fix(branch): make branch delete correct under partial failure (#137)

* test(lance): pin force_delete_branch surface guard

Pin the Lance 6.0.1 force_delete_branch behavior the branch-delete
single-authority redesign relies on: plain delete_branch errors on a
missing ref, force_delete_branch removes an existing forked branch, and
the local-store quirk where force_delete on a fully-absent branch still
errors (worked around by the upcoming TableStore::force_delete_branch).

Re-pin the docs/dev/lance.md alignment stanza (9 guards; 4 runtime).

* feat(storage): add force branch-delete to TableStore + CommitGraph

Add TableStore::force_delete_branch and CommitGraph::force_delete_branch
(idempotent: tolerate an already-absent branch via Lance RefNotFound /
NotFound), plus CommitGraph::list_branches for the cleanup reconciler to
diff against the manifest authority. RefConflict (referencing
descendants) is still surfaced. Unused until the branch-delete rewire.

* test(maintenance): red — cleanup reconciles orphaned branch forks

Forge a Lance branch on the Person table that the manifest never
references (a zombie fork from an incomplete prior delete) and assert
cleanup reclaims it while leaving main intact. Fails today: cleanup does
not yet reconcile orphaned forks. Goes green with the next commit.

* fix(maintenance): reconcile orphaned branch forks in cleanup

Add reconcile_orphaned_branches: force_delete_branch every per-table and
commit-graph Lance branch absent from the manifest branch set (the
authority), children-before-parents. Folded into cleanup_all_tables,
runs before version GC. Idempotent and authority-derived; no-ops once
nothing is orphaned, and would harmlessly find nothing if a future Lance
atomic multi-dataset branch op prevented orphans. Adds TableStore::list_branches
and exposes graph_commits_uri(pub crate). Turns the maintenance red test green.

* test(failpoints): red — branch_delete partial failure converges

Add the branch_delete.before_table_cleanup failpoint hook (inert without
the feature) and a regression test: a cleanup-step failure after the
manifest authority flip must leave branch_delete returning Ok, the branch
gone, the orphan stranded, then reclaimed by cleanup, and the name
reusable. Fails today: cleanup_deleted_branch_tables propagates the error
as a hard failure. Goes green with the next commit.

* fix(branch): best-effort fork reclaim after the manifest flip

Make branch_delete treat per-table forks and the commit-graph branch as
derived state reclaimed best-effort with force_delete_branch after the
manifest authority flip. A reclaim failure (transient error, or the
branch_delete.before_table_cleanup failpoint) is logged via tracing::warn
and swallowed: the branch is already gone and the cleanup reconciler
converges the orphan. cleanup_deleted_branch_tables no longer returns an
error or blocks the call. Turns the partial-failure recovery test green.

* test(failpoints): red — recreate over orphaned fork is actionable

After a partial-failure delete leaves a fork orphaned, recreating the
branch name and writing to the previously-forked table before cleanup
runs currently surfaces the opaque ExpectedVersionMismatch ("stale view
... expected manifest table version N"). Assert instead a clear error
pointing the user at cleanup. Goes green with the next commit.

* fix(branch): actionable orphan-collision error in fork_branch_from_state

When a fork's create_branch collides with an existing target ref, reuse
it only if its head matches source_version (a legitimate concurrent
first-write). A version mismatch means a zombie fork from an incomplete
prior delete: return a manifest_conflict pointing the user at
`omnigraph cleanup`, instead of the opaque ExpectedVersionMismatch.
Turns the recreate-over-orphan red test green.

* docs(invariants): single-authority branch-lifecycle + Lance forward-compat

Record branch delete in the Current Truth Matrix: manifest is the single
authority flipped atomically first, per-table forks + commit-graph branch
are derived state reclaimed best-effort with the cleanup reconciler as
backstop, and reusing a name whose reclaim failed surfaces an actionable
error. Note the reconciler is authority-derived and degrades to a no-op
under a future Lance atomic multi-dataset branch op, the same shape as
invariant 7.

* test(failpoints): red — cleanup isolates a single-table failure

Add the cleanup.table_gc failpoint hook (inert without the feature) and
an error: Option<String> field on TableCleanupStats (mechanical, always
None for now). Regression test: a one-shot version-GC failure for one
table must not abort the whole cleanup — assert cleanup still succeeds,
surfaces the failure per-table in stats, and the independent reconcile
pass still reclaimed an orphan. Fails today: the version-GC collect
aborts on the first table error. Goes green with the next commit.

* fix(maintenance): fault-isolate cleanup per table

Make the cleanup sweep do as much as it can and converge on re-run
instead of aborting wholesale on one table's transient error
(invariant 13). The version-GC loop now records a per-table failure on
its stats row (error: Some) and logs it rather than collecting into a
Result that aborts; reconcile_orphaned_branches isolates per-table and
commit-graph failures into BranchReconcileStats.failures. The CLI reports
any failed tables and tells the user to rerun cleanup. Addresses the
Devin review finding. Turns the single-table-failure test green.

* test(failpoints): red — branch_create heals commit-graph zombie + is atomic

Add the branch_delete.before_commit_graph_reclaim failpoint hook and two
regression tests: (a) recreating a name whose delete left a commit-graph
zombie must succeed (today it dies on Lance's internal Clone error), and
(b) branch_create must roll back the manifest branch when the derived
commit-graph branch fails (today it leaves the manifest branch created
while returning Err). Both fail now; green with the next commit. The
existing branch_create_failpoint_triggers test still passes.

* fix(branch): make branch_create atomic + heal commit-graph zombie

branch_create now flips the manifest authority first, then creates the
derived commit-graph branch in create_commit_graph_branch, force-dropping
any orphaned commit-graph ref left by an incomplete prior delete (the
manifest branch is fresh, so a same-named commit-graph branch is provably
a zombie). If commit-graph creation fails, the manifest branch is rolled
back so the name never half-exists. Addresses the Codex review finding.
Turns the two branch_create red tests green; existing tests unaffected.

* test(failpoints): red — fork collision misclassifies live concurrent fork

Add the fork.before_classify failpoint hook and a concurrency test: when
a concurrent first-write legitimately wins the fork race, the loser must
get a retryable refresh-and-retry, not the misleading run-cleanup orphan
error. Today the version-comparison misclassifies the live fork as an
orphan (the Cursor finding). Goes green with the next commit.

* fix(branch): manifest-arbitrated fork-collision classification

Classify a fork collision by the manifest authority instead of comparing
Lance branch versions. Before forking, open_owned_dataset_for_branch_write
re-reads the live manifest: if the table is already forked on the active
branch, a concurrent first-write won and the loser gets a retryable
refresh-and-retry (not a misleading orphan error). fork_branch_from_state
no longer guesses from versions — a create collision past that check is
an orphan, so it returns the actionable cleanup error. Addresses the
Cursor finding; turns the live-concurrent-fork test green, zombie path
unchanged.

* test(failpoints): close branch-lifecycle test gaps

Three coverage additions for the branch-delete work (behavior already
correct; these lock it in and catch regressions):

- cleanup_isolates_reconcile_failure: inject a force-delete failure into
  the reconcile loop (new cleanup.reconcile_fork hook) and assert the
  sweep continues + converges on re-run. Directly covers the reconcile
  loop the Devin finding was about (previously only version-GC was).
- cleanup_reclaims_orphaned_commit_graph_branch: forge a commit-graph
  orphan via the delete reclaim failpoint and assert cleanup's
  reconcile_commit_graph_orphans drops it (previously untested).
- fork_collision_with_live_concurrent_fork_is_retryable: replace the
  fixed 300ms sleep with a deterministic readiness signal (cfg_callback +
  compare_exchange atomics) so the two-writer ordering can't flake.

Full failpoints suite 31/0.

docs/dev/invariants.md

@@ -99,6 +99,7 @@ Use it this way:
 | Multi-table commit | Manifest CAS plus recovery sidecars; not a single Lance primitive | [writes.md](writes.md), [architecture.md](architecture.md) |
 | Constructive mutations | In-memory `MutationStaging`, one end-of-query table commit per touched table, then one manifest publish | [writes.md](writes.md), [execution.md](execution.md) |
 | Deletes | Inline-commit residual; delete-only queries allowed, mixed insert/update/delete rejected by D2 | [query-language.md](../user/query-language.md), [writes.md](writes.md) |
+| Branch delete | Manifest is the single authority, flipped atomically first; per-table forks + commit-graph branch are derived state, reclaimed best-effort (`force_delete_branch`) with the `cleanup` reconciler as the guaranteed backstop. Reusing a name whose reclaim failed before `cleanup` surfaces an actionable error | [branches-commits.md](../user/branches-commits.md), [maintenance.md](../user/maintenance.md) |
 | Schema validation | Type checks, required fields, defaults, edge endpoint checks, and edge cardinality are enforced on write paths | [schema-language.md](../user/schema-language.md), [execution.md](execution.md) |
 | Unique constraints | Intra-batch and write-path checks exist; full cross-version uniqueness is still a gap | [schema-language.md](../user/schema-language.md) |
 | Storage trait | `TableStorage` exists as the sealed staged-write surface; full call-site migration and capability/stat surfaces are incomplete | [writes.md](writes.md), [architecture.md](architecture.md) |
@@ -107,6 +108,13 @@ Use it this way:
 | Auth | Bearer token hashing and server-side actor resolution are implemented at the HTTP boundary | [server.md](../user/server.md), [policy.md](../user/policy.md) |
 | Tests | Tempdir-backed Lance tests are the current substrate; there is no `MemStorage` test backend | [testing.md](testing.md) |
 
+The branch-delete reconciler is authority-derived: it reclaims orphaned forks
+today and degrades to a no-op if Lance ships an atomic multi-dataset branch
+operation, so the design composes with that future rather than blocking it. This
+is the same shape as invariant 7 (indexes are derived state); prefer it over a
+recovery-sidecar-style approach for any new multi-dataset metadata operation,
+since the sidecar would be scaffolding to remove once the substrate closes the gap.
+
 ## Known Gaps
 
 Do not hide these behind invariant wording. Either move them forward or keep

docs/dev/lance.md

@@ -175,7 +175,8 @@ Migration from Lance 4.0.0 → 6.0.1 landed in this cycle (DataFusion 52 → 53,
 - **Lance #6658 closed** (2026-05-14) but `DeleteBuilder::execute_uncommitted` did **not** ship in v6.0.1 — binary search across the release stream shows it first appears in `v7.0.0-beta.10` (the closing commits landed on main but didn't backport to the 6.x line). Tracked as MR-A: migrate `delete_where` to staged, retire the parse-time D2 mutation rule, extend recovery sidecar coverage. **Gated on the Lance v7.x bump**, not this PR. v7.0.0-rc.1 dropped 2026-05-21.
 - **Lance #6666 still open** (`build_index_metadata_from_segments` public): vector-index two-phase blocked; inline `create_vector_index` residual retained.
 - **Lance #6877 still open** (`MergeInsertBuilder` dup-rowid): PR #109's `SourceDedupeBehavior::FirstSeen` + `check_batch_unique_by_keys` precondition stay load-bearing.
+- **`Dataset::force_delete_branch`** (`branches().delete(name, force=true)`, dataset.rs:524) tolerates a missing branch-*contents* ref (vs plain `delete_branch`'s `RefNotFound`), but on the local store still errors `NotFound` if the branch `tree/` directory is fully absent (`remove_dir_all`'s NotFound is not caught for Lance's native error variant, refs.rs:526-549). Both variants still refuse a branch with referencing descendants (`RefConflict`). `TableStore::force_delete_branch` wraps this to be fully idempotent (tolerates already-absent). The single-authority branch-delete redesign uses it for orphan reclamation (eager best-effort reclaim + cleanup reconciler). Pinned by `lance_surface_guards.rs::force_delete_branch_semantics`. Branch delete is "flip the ref atomically, then `remove_dir_all(tree/{branch})`"; branch-exclusive data lives under `tree/{branch}/` so a drop reclaims it immediately without touching `main`.
 
-Surface guards added: `crates/omnigraph/tests/lance_surface_guards.rs` (8 named guards; 3 runtime + 5 compile-only). Future Lance bumps re-run this file first as the smoke check. Two additional guards from the original plan deferred to follow-up (`manifest_cas_returns_row_level_contention_variant` needs full publisher-race harness; `table_version_metadata_byte_compatible_with_v4` needs `pub(crate)` reach extension).
+Surface guards added: `crates/omnigraph/tests/lance_surface_guards.rs` (9 named guards; 4 runtime + 5 compile-only). Future Lance bumps re-run this file first as the smoke check. Two additional guards from the original plan deferred to follow-up (`manifest_cas_returns_row_level_contention_variant` needs full publisher-race harness; `table_version_metadata_byte_compatible_with_v4` needs `pub(crate)` reach extension).
 
 Bump this date stanza on the next alignment pass.